Crystal rectifier tube



Jan. 15, 1963 D. A. LANClANl CRYSTAL RECTIFIER TUBE Original Filed 001;. I1, 1955 IN V EN TOR.

{ ATTORNEYS United States Patent Ofifice 3,074,022 Patented Jan. 15, 1963 3,974,022 CRYSTAL RECTIFIER TUBE Daniel A. Lanciani, West Medford, Mass, assignor t Microwave Associates Inc, Boston, Mass, a corporation of Massachusetts Original application (Pct. 11, 1955, Ser. No. 539,786, new Patent No. 2,945,122, dated .luiy 12, 1960. Divided and this application June 23, 1959, Ser. No. 822,716

6 Claims. (Cl. 329-162) The subject invention relates to a mixer crystal rectifier tube and particularly to a rectifier crystal tube for coupling a rectangular Wave guide to a rectifier crystal in the millimeter Wave length region. This application is a division of application Serial No. 539,786 filed October 11, 1955, now Patent No. 2,945,122 issued July 12, 1960.

Mixer crystal rectifiers designed for the lower microwave frequencies and of a convenient size and shape have been constructed for use with both coaxial and wave guide mounting arrangements. As the wave' length decreases below one centimeter, however, it has been found impractical to scale down the traditional coaxial designs. For example, the 1N53 type of crystal coaxial cartridge for l-centimeter use is limited to an inner diameter of .045 inch and an outer conductor diameter of .125 inch in order that the cut-off wave length of the next higher mode (TE-11) in the coaxial section would be substantially less than on the lowest anticipated operating wave length. This provided a resulting cut-ofl wave length for the cartridge of .635 centimeter which was well below the expected operating range for the design.

However, application of the same considerations in the 4 millimeter region results in inner and outer conductor diameters of .023 inch and .063 inch respectively. These dimensions are obviously too small to be practical. It is therefore proved necessary to design new types of wave guide mounted crystals for rectifier use in the millimeter region. One such device has been suggested by Dr. G. C. Southworth in his book, Principles and Applications of Wave Guide Transmission, Van Nostrand Co., New York, 1950, on page 653 (Chapter 12). In this design the crystal is mounted in a cylindrical metal housing or cartridge which couples to the rectangular guide through a hole in the side of the cylindrical housing. An adjustable plunger on one side of the cavity in the cylindrical housing carries the crystal and a whisker projects across the opening to the crystal.

It is the object of this invention to provide an improved and more easily manufactured millimeter rectifier tube of convenient size and a construction which may be readily assembled.

It is a feature of this invention that it utilizes a hollow metallic cylinder or cartridge to house the rectifier, said cartridge being adapted to propagate the TE-ll mode of round wave guide, together with an inner circular to coaxial transition assembly which feeds energy to the whisker silicon junction. A further feature of this invention is the use of a dielectric end seal adjacent the rectangular wave guide to which this assembly is mounted. This dielectric seal functions as a matching transformer be tween the rectangular guide and the cartridge whereby the position of the remaining RF portions of the rectifier are rendered more or less independent of their distance from the junction. It is a still further feature of this invention that it provides improved and simplified means for RF choking and capacitive by-passing of the IF output lead.

This invention will be more easily understood by reference to the following figures:

FIG. 1 illustrates a cut-away elevation of the entire rectifier tube assembly.

FIG. 2 is a cross-section through the case and retaining shell showing the positioning key. v v

FIG. 3 shows the dominant TE-IO mode configuration in a rectangular wave guide.

FIG. 4 shows the dominant TE-ll mode in a circular wave guide.

FIG. 5 shows the electric field configuration in the vicinity of the converting fin.

As illustrated by reference to FIGS. 1 and 2 this invention utilizes a cylindrical case or cartridge 10 appropriately mounted to an opening 11 in a rectangular wave guide section 12. As illustrated the cartridge is mounted coaxially with the rectangular guide but it would also be appropriate to mount the device on the side of a rectan-.

gular section having a tuning end plunger. For convenience the case 10 is held by a cylindrical shell 13 having an end flange 15 which is fastened to the end flange of the rectangular guide. The other end of the shell carries a bayonet structure 23 to mate with a standard BNC connector thereby joining a coaxial line to the output end of the crystal tube. Thus the tube is shielded separable insert which may be easily replaced if the crystal should burn out. The bayonet connector tends to press the tube into firm contact with the waveguide end. The key 14 projecting from the inside of the shell fits into the slot 17 in the case thereby aligning the case, including in particular the mode converting fin to be described later, with respect to the TE-IO mode in the rectangular guide. While direct coupling is shown between the end of the rectangular guide and the end of the case, a quarter-wave choke coupling may under some circumstances be desirable. The key and slot structure would tend to interfere with the operation of such a choke joint if located near the center of the top or bottom of the rectangular guide. Therefore this structure may in some cases be located at the side where the electric field is at a minimum. To assure proper alignment of the shell and key the pin 19 on the shell is fitted to the hole 21 in the end flange of the rectangular guide. J The dielectric plug 16 is fitted to the end of the case '10 adjacent the junction with the rectangular wave guide 12. It is the function of this plug to act as a moisture-sealing window and at the same time to serve as a junction matching device. If this dielectric plug were made to have an effective length of one-half wave length, the window would be reflectionless within the circular wave guide portion of the case 10 adjacent the rectangular guardl However, the RF impedance mismatch created by the junction would then have to be compensated with proper dimensioning of the remaining whisker silicon geometry. This would have the critical disadvantage of requiring these rectifying elements to be precisely located a specified distance from the junction and in addition the relatively large distance between the junction reflection and the compensating reflection of the whisker would tend to make the unit frequency sensitive.

The window 16 is therefore preferably designed to have an effective length of one-quarter wave length of the TE-ll mode in the circular guide 10. In the 4 millimeter region this dimension should be accurate to within .001". In addition the plug element 16 is designed to have a characteristic impedance which is the geometric mean between the impedance of the rectangular wave guide 12 and the circular wave guide element or section 10. Described mathematically Where Z is the impedance of the filled circularguide and Z and Z the impedances of the air filled rectangular and circular guides respectively. The wave length of dielectric filled circular guide may be closely approximated 3 by multiplying the wave length in air filled circular guide by where K is the dielectric constant. For use in the millimeter wave region, it has been found that Teflon having a dielectric constant of approximately 2.15 is an appropriate material to lower the impedance of the circular wave guide by reducing the wave guide length to the geometric mean of air-filled rectangular and circular plane guide elements. In addition, it has low loss properties in the millimeter wave length region and a plug of the shape shown by reference to element 16 may be pressfitted to the case to effect a suitable moisture-sealing gasket in a very simple manner. As shown in FIG. 2 the inside diameter of the case 10 is as large as or larger than the diagonal between opposite corners of the rectangular guide.

To connect the circular wave guide section to the silicon junction an additional transition element 18 in the form of a circular to coaxial transition fin is utilized. This fin is mounted for ease of assembly in a cylindrical conductive section 20 which may be press-fitted into the cylindrical interior of case 10 to appropriately position the fin 18 with respect to the plug 16'. To provide a compact design, the fin is positioned adjacent to the plug 16 and the conductive cylinder 20 is rotated in position about the axis of the tube 10 to appropriately align fin 18 with respect to the TE-lO mode propagating in the rectangular guide 12. Since the cartridge is a separable unit the fin is actually oriented with respect to the aligning element 14 on the exterior of the case 10 so that upon assembly with the rectangular wave guide the fin will be appropriately oriented.

The fin 18 is preferably in the form of a triangular slab having parallel sides, a front face sloping upward away from the front of the cartridge at an angle of approximately 45 with the axis and having a substantially vertical rear face in the same plane as the end of the cylindrical supporting section 20. The pure silicon wafer is mounted on a raised boss projecting on the order of V from the rear face of the fin 18 on the axis of the tube 10. It has been found that a circular to coaxial transition of this type is substantially more efficient than a more. conventional form of coupling loop, although it will be. apparent that other circular to coaxial transition elements might be used. The crystal mounting in addition serves as a DC. ground return for the rectifier since the boss 22 and elements 18, 20 and 10 are all conductive.

To the rear of the cylindrical section 20 is a cylindrical a spacer 24 which serves to. appropriately and conveniently space the IF output section of the tube from the silicon dice, particularly during assembly. This spacer is preferably of thin material to avoid interfering with the coupling between the whisker and the cavity surrounding it. The spacer may be of metal provided that it is not thick enough to short out the plunger 28 to the case 10.

Adjacent and abutting this spacer is the cylindrical insulating sleeve 26 surrounding the cylindrical plunger 28 which contains provisions for RF choking and capacitive by-passing of the IF output section. This plunger is of conductive material and its preferred embodiment carries two flanges 30 and 32. The second flange 32 is carried within a channel in the insulating sleeve 26 thereby permitting the plunger to be snap-fitted to this insulating sleeve. To prevent the passage of RF power to the IF output section, as mentioned above, the displacement between the front face of the first flanges and the inner cylindrical surface of the groove is effectively one-half wave length, taking into account the dielectric constant of the insulating material 26. The capacitance between the surface of the plunger and the inner wall of the case is designed to be approximately seven microfarads for 4 millimeter operation. V i

The plunger 28 is cylindrical and has a cylindrical internally threaded opening 34. A metal pin preferably in the form of two sections 36 and 38 are threaded to fit this opening. The threaded pin 36 carries on its forward end the whisker 40 having a sharpened point which makes contact with the silicon wafer. The whisker 40 has a bent center section in the form of a helical spring which prevents the pressure on the upper point against the wafer to be adjusted Without any tendency for the point to slide off its location on the axis of the case 10. The pressure of this contact is adjusted by rotating the pin 36 to screw it into the cavity 34 the required distance. A slot 42 is provided in the back of this pin to facilitate this adjustment. When this adjustment has been made the second section of the pin 38 is screwed into the cavity and serves to lock the first pin in position. This second pin 38 projects backward into the rear section of the cylindrical housing pin to provide a suitable IF output connection.

In operation the above described millimeter Wave rectifier operates as follows. Microwave power propagating in the rectangular wave guide 12 in the form of energy in the dominant TE-lt] mode as illustrated in FIG. 3 is efliciently transformed with the aid of the dielectric matching window 16 into the TE-ll mode operating the forward part of the circular cartridge 10, as illustrated by reference to FIG. 4. This circular TE-ll mode is thereafter intensified in the center of the case by the coupling loop in the form of a triangular fin 18. The electric field intensity and distribution is shown approximately in FIG. 5. Coupling between the RF field and the junction is accomplished in the cavity surrounding the whisker. The intense field in the region of the fin tends to bend parallel to the whisker after passing away from the transition fin. While the mode configuration is complex and the mode is not purely coaxial in form it is similar to coaxial propogation and the fin may be conveniently designated as a circular to coaxial transition fin. The propagation of RF power into the IF output section is blocked by the operation of the flange choking element 28 which is formed as an integral part of the IF output.

While the presently preferred embodiment utilizes the above-described coupling loop in which the silicon wafer is mounted to the transition fin and the whisker to the pin, it would be obviously possible to reverse this arrangement and mount the whisker to the fin and the silicon wafer on the pin. Such an arrangement would increase the di'splacernent of the silicon from the trailing edge of the transistion fin and this displacement has already proven effective in improving performance at some frequencies. The entire device may be easily assembled since all of the parts are in the form of cylindrical elements which may be fitted to the inside of the cylindrical case and the case 10 in turn is grooved to permit appropriate alignment of the tin 18 with respect to the rectangular wave guide 12.

While this invention has been described with respect to a single embodiment it Will be understood that the exact construction of the invention may be varied by those skilled in the art without departing from the scope of this invention as described in the following claims.

I claim:

1. A crystal cartridge comprising an outer conductor, cooperating semiconductor and rectifying elements, means supporting said cooperating elements in fixed position Within said outer conductor, the supporting means for one of said elements comprising an electrically conductive plug within said outer conductor, a layer of dielectric material filling the space between said plug and said outer conductor, said plug incorporating radio frequency choke means including an integral electrically conductive element projecting laterally therefrom toward said outer conductor, said dielectric material being grooved to receive said choke element whereby said choke element can serve simultaneously as a mechanical retainer for said plug, and means providing a direct current path from one of said elements to said outer conductor.

2. A crystal cartridge comprising an outer conductor, cooperating semiconductor and rectifying elements, means supporting said cooperating elements in fixed position within said outer conductor, the supporting means for one of said elements comprising an electrically conductive plug within said outer conductor, a layer of dielectric material filling the space between said plug and said outer conductor, said plug incorporating radio frequency choke means including an integral electrically conductive element projecting laterally therefrom toward said outer conductor, said dielectric material being grooved to receive said choke element whereby said choke element can serve simultaneously as a mechanical retainer for said plug, and means including the supporting means therefor providing a direct current path from the other of said elements to said outer conductor.

3. A crystal cartridge comprising an outer conductor, cooperating semiconductor and rectifying connection elements, means supporting said cooperating elements in fixed position within said outer conductor, means providing a direct current path from one of said elements to said outer conductor, the supporting means for the other of said elements comprising an electrically conductive plug within said outer conductor, a layer of dielectric material filling the material between said plug and said said outer conductor, said plug incorporating radio frequency choke means including an integral electrically conductive element projecting laterally therefrom toward said outer conductor, said dielectric material being grooved to receive said element, whereby said choke element can serve simultaneously as a mechanical retainer for said plug.

4. A crystal cartridge comprising an outer cylindrical conductor, cooperating semiconductor and rectifying elements, means supporting said cooperating elements in fixed position within said outer conductor, the supporting means for one of said elements comprising an electrically conductive cylindrical plug within said outer conductor, a sleeve of dielectric material filling the space between said plug and said outer conductor supporting said plug relative to said outer conductor, said plug incorporating radio frequency choke means including an integral electrically conductive annular element projecting laterally therefrom toward said outer conductor, said dielectric material being grooved to receive said choke element whereby said choke element can serve simultaneously as a mechanical retainer for said plug, and means providing a direct current path from one of said elements to said outer conductor.

5. A crystal cartridge comprising an outer cylindrical conductor, cooperating semiconductor and rectifying elements, means supporting said cooperating elements in fixed position within said outer conductor, the supporting means for one of said elements comprising an electrically conductive cylindrical plug within said outer conductor, a sleeve of dielectric material filling the space between said plug and said outer conductor supporting said plug relative to said outer conductor, said plug incorporating radio frequency choke means including an integral electrically conductive annular element projecting laterally therefrom toward said outer conductor, said dielectric material being grooved to receive said choke element whereby said choke element can serve simultaneously as a mechanical retainer for said plug, and means including a circular to coaxial coupling loop providing a direct current path from one of said elements to said outer conductor.

6. A crystal cartridge comprising an outer cylindrical conductor, cooperating semiconductor and rectifying elements, means supporting said cooperating elements in fixed position Within said outer conductor, the supporting means for one of said elements comprising an electrically conductive cylindrical plug within said outer conductor, a sleeve of dielectric material filling the space between said plug and said outer conductor supporting said plug relative to said outer conductor, said plug incorporating radio frequency choke means including an integral electrically conductive annular element projecting laterally therefrom toward said outer conductor, said dielectric material being grooved to receive said choke element whereby said choke element can serve simultaneously as a mechanical retainer for said plug, the supporting means for the other of said elements including a circular to coaxial coupling loop providing a direct current path from said other element to said outer conductor.

References Cited in the file of this patent UNITED STATES PATENTS 2,673,930 Matare Mar. 30, 1954 2,788,497 Osial et al Apr. 9, 1957 2,834,884 Domenichini et a1. May 13, 1958 2,840,710 Levy June 24, 1958 FOREIGN PATENTS 661,969 Great Britain Nov. 28, 1951 

1. A CRYSTAL CARTRIDGE COMPRISING AN OUTER CONDUCTOR, COOPERATING SEMICONDUCTOR AND RECTIFYING ELEMENTS, MEANS SUPPORTING SAID COOPERATING ELEMENTS IN FIXED POSITION WITHIN SAID OUTER CONDUCTOR, THE SUPPORTING MEANS FOR ONE OF SAID ELEMENTS COMPRISING AN ELECTRICALLY CONDUCTIVE PLUG WITHIN SAID OUTER CONDUCTOR, A LAYER OF DIELECTRIC MATERIAL FILLING THE SPACE BETWEEN SAID PLUG AND SAID OUTER CONDUCTOR, SAID PLUG INCORPORATING RADIO FREQUENCY CHOKE MEANS INCLUDING AN INTEGRAL ELECTRICALLY 